1. Field of the Invention
This invention relates to an original-reading device which illuminates an original and reads image light from the orginal with a reading sensor, such as a photoelectric conversion device or the like.
2. Description of the Related Art
A device which iluminates a sheet-like original with an illuminating light source, images light reflected from the surface of the original onto a reading sensor device using an optical system, and performs photelectric conversion of the image to obtain signal information has been widely used in devices, such as a facsimile, a copier, an image scanner or the like. In this kind of apparatus, a cylindrical lens has generally been used as an imaging lens, which results in a small apparatus. Recently, for the purpose of providing a small apparatus, a contact sensor, which incorporates and confines a rod array lens together with an illuminating light source and a unit-magnification reading sensor as one body, has been produced and rapidly propagated.
FIG. 4 shows a cross-sectional view of this kind of reading device as a conventional example. A contact sensor 201 of the device includes a light source 301, an imaging lens 501 and a photosensor 601. A transparent glass body 401 is provided at the side of an optical path used for a reading operation, and a surface of the glass body 401 is made an imaging surface. An original to be read is made to contact the imaging surface, and information is read while feeding the back of the original with a rotating roller 101. This apparatus can be more or less satisfactorily used for reading information, such as characters or the like, to obtain binary-coded signal information. However, recent demand from the market has become more severe, and a scanner capable of reading information in an original having gradation, such as a photograph or the like, with a high picture quality has been demanded. In order to respond to such a demand, a method is currently adopted in which the above-described rotating roller is made white, the white background on the surface of the rotating roller is read before reading information from an original to provide a reference for white balance correction, an original having an image with gradation is then read, and the information from the original is corrected in accordance with the correction. Although this method is good for inputting information having lower gradation, a stain in the white reference has become a big problem for high picture quality (high gradation). That is, the outer circumferential surface of the roller rotates in contact with the surface of the glass when an original is not present. The surface of the roller can become stained or may produce a worn-out powder while repeating such rotation, causing a stain on the imaging surface of the glass. Although it is possible to periodically clean the surface of the glass, the surface of the roller can not always be restored to the white reference level present at the initial stage even if it has been cleaned. Hence, the above-described method has the disadvantage that a reading device for reproducing high picture quality cannot be provided.
Several countermeasures have been considered for solving the above-described problem in the prior art. They are, for example, selection of an abrasion-resistive material which does not produce the phenomenon of abrasion of the rotating roller even if there is abrasive slippage with the surface of the glass, improvement in materials, such as a reduction of the coefficient of friction (.mu.) between the rotating roller and the surface of the glass causing abrasion, a mechanical method, such as separating the surface of the roller from the surface of the glass when an original to be read is not present so that the phenomenon of friction is not produced at all, and the like. One must say, however, that a complete solution directed to the materials is very difficult to achieve. The separation of the roller results in a complicated and expensive configuration. Hence, none of the above-described approaches are effective means for solving the problems. Even if one of the above-described methods is adopted and abrasion of the rotating roller is thereby reduced, there is the problem that the original to be read itself introduces dust from the surroundings causing stain, which stains the surface of the roller with the lapse of time.